The issue that has always been with remaps, is if you generate ECU codes.
Depending on the level of recalibration you may find the ECU logging all sorts of stuff.
Boost target anomolies, excess MAP etc etc.
And you just wont know unless you have the tools to check, read and erase them.
So be very careful.
The latest ECUs even have error flags labelled "tuner box detect" etc

They are indeed quite complex, and as with anything its a gamble with the waranty.